Note Added in Proof
While this manuscript was under review, Ballew et al. published a paper entitled “Germline mutations of regulator of telomere elongation helicase 1, RTEL1, in dyskeratosis congenita” (Hum. Genet., published online January 18, 2013). This paper documents one family affected by biallelic RTEL1 mutations causing HHS and two families affected by heterozygous RTEL1 mutations (causing HHS in one and causing DC in the other). Although the family afflicted with biallelic RTEL1 mutations is similar to the seven families described in this study, the pathogenic role of the heterozygous RTEL1 mutations in the other two families is unclear.